Film casting apparatus



Dec. 27, 1.960 CROSBY T AL 2,965,927

FILM CASTING APPARATUS 3 Sheets-Sheet 1 Filed Dec. 30, 1958 INVENTORS BYATTORNEY Dec. 27, 1960 CROSBY ET AL 2,965,927

' FILM CASTING APPARATUS Filed Dec. 30, 1958 3 Sheets-Sheet 2 INVENTOR5AZZaw Z. Crafy [(Zmraelk/Z'fiai TTORNEY A. L. CROSBY ETAL FILM CASTINGAPPARATUS Dec. 27, 1960 Filed Dec. 50, 1958 3 Sheets-Sheet 5 INVENTORSATTORNEY Unite States FILM CASTING APPARATUS Filed Dec. 30, 1958, Ser.No. 783,788

Claims. (CI. 18-15) This invention relates to film forming andparticularly to the forming of thin films containing the triplecarbonates of barium, calcium and strontium in a cellulosic binder anduseful as emissive coating material in electron tubes.

These films are intended to be cut to size to fit about cathode sleevesemployed in electron tubes. For such usage it is highly desirable thatthe films shall have smooth surfaces and be of uniform thinness so thatthe coated cathode sleeve can be placed exceedingly close to the nextadjacent electrode element, such as a grid, without danger of physicalcontact of portions of its surface with said element. Also to secureuniformity of emissive quality, the coating should be of uniformthinness throughout. This is particularly true where films of the orderof .001 inch are to be formed. To form films of this thinness specialforms of film casting apparatus is necessary so that first, such filmsmay be formed on the apparatus and second, that such films may beremoved from the apparatus without tearing or breaking of the film orthe forming of holes therein.

It is an object of this invention to provide an apparatus which shallform a film of even thinness throughout.

It is a more specific object of the invention to provide a means forensuring the even feeding of a suspension of the triple ncarbonates in aplastic binder to a polished moving surface and for the fine adjustmentof said means to secure the desired thinness of the cast film.

Another specific object is to ensure the absolute cleanliness of thesurface upon which the film is to be cast to prevent unevennesses in thefilm.

Other objects of the invention will become apparent upon considerationof the following specification when taken in conjunction with theaccompanying drawing in which:

Fig. 1 is a schematic presentation of a film forming system embodyingthe invention.

Fig. 2 is a section on the line 2-2 of Fig. 1.

Fig. 3 is a side elevation of a portion of the film casting mechanism.

Fig. 4 is a section through the mechanism of Fig. 3 in a plane parallelto the plane of the paper.

Fig. 5 is a section on the line 5-5 of Fig. 3.

Fig. 6 is a plan view of the film casting apparatus, parts being shownin section.

Fig. 7 is a view of the film casting apparatus looking at Fig. 6 fromthe right, and

Fig. 8 is a section on the line 8-8 of Fig. 7.

Referring to the drawings with greater particularity, at 10, Fig. 1, isdisclosed a metallic hopper containing the triple carbonates suspendedin a volatile cellulosic solution, for example, ethylcellulose dissolvedin a mixture of toluene, ethanol and pentacetate, all as is set forthmore in detail in the application of Kerstetter and Wennin Serial No.453,235, filed August 31, 1954, and assigned to the assignee of thisapplication. The hopper is of course open at its bottom and is air tightat the top except for a valve 12 which may be opened to vent the sysa2,965,927 .a tented Pa; 37' #369 tem. A piping 14, 15, conveys thesuspension to the hopper from a mixing tank 16 provided with a motordriven stirrer 18 to maintain the mixture homogeneous; and the surfaceof the mixture is maintained under air pressure, as through a constantpressure air regulator valve 20. The pipe 15 has its inlet opening belowthe surface of the mixture in the mixing tank. The mixture in the hopperis fed onto a casting wheel 22 in the form of a narrow cylinder mountedon a horizontal axle 24 driven in any well known manner at a rate togive a peripheral speed of about one and one half feet per second. Thesurface of the wheel is of highly polished nickel steel and ismaintained scrupulously clean by a water soaked sponge 26 with water fedthereto from a water pipe 27, and rotating in an opposite sense to therotation of the wheel in order to sponge off any dust or dirt on thesurface of the wheel; a drain 28 beneath the sponge catches the excesswater which is led off through a suitable drain hose 29. The apparatusitself should be installed in a dust free room. There is also provided aliquid applicator in the form of a drum 38 comprised of a shaft 31 onwhich are strung a very large number of thin discs 32 of polyethylenefilm held together between end discs 34 of Lucite by nuts 35 threaded onthe shaft at the ends of the drum. The discs dip into a tank 36 ofliquid which will act as a release agent for the carbonate film from thecasting wheel 22, as for example, 2,2-aminomethylamino ethanol (NH CHCI-I NHCH CH 0H) which has a boiling point of about 130 C. at a pressureof twelve millimeters of mercury, and the thinness of the film of liquidcan be adjusted very minutely by loosening or tightening the Lucitediscs on the shaft or by shifting the axle carrying the polyethylenediscs 32 away from or towardthe surface of the wheel. This shifting maybe accomplished by means of a differential screw 38 having a knurled nut39, the screw being threaded into a lug 40 extending down from the tank36 and into a threaded bearing 41 on the base 42 of the machine, thetank 36 being suitably guidedly supported for sliding movement on saidbase as by its support post 43 sliding between two dovetailed straps 44.The shaft 31 is driven through a motordriven slow speed gearing 45, thegearing being of the variable character to provide further means to varythe speed of the shaft 3-1 and therefore the quantity of liquid appliedby the applicator to the wheel. Above the applicator is a pair ofvertically spaced heating lamps 46 to preliminarily heat the polishedsurface of the wheel. Thus, the amount of liquid remaining on the wheeldepends, in part, on the choice of rotational speed of the wheel and onthe heat cast by the lamps 46 onto the wheel. The lamps are intended toleave a small amount of liquid on the wheel to assist in the subsequentpeeling of the cast film from off the wheel. The wheel comprises acentral drum 47 of iron or the like having a rim 48 of a highly polishedmetal such as nickel or chrome to afford a smooth highly polishedsurface, although nickel steel is preferred.

After the film has been cast on the wheel by flow of material from thehopper 10, either by action of gravity alone, or by the action ofgravity assisted by air pressure, the film passes beneath an open orperforated bottom box 50 which has air fed thereto by pipe 52. Anysuitable form of heater, as finned electric resistance rods 53', isembodied within the box and the air in passing over and about the heateris heated, is blown out of the open or perforated bottom of the box andonto the freshly cast film of carbonates. The film by the time itreaches the line of stripping off which approximately is at the positionI indicated by the reference character 60 has sufiicient of '9 itsvolatile solvents driven olf so that the film has enough tenacity to bepulled from off the drum and deposited ontoanendless mesh conveyor belt62 travelling in the direction of the arrow in Fig.1. The filni isstripped off the casting wheel by the pullof the conveyor belt, assistedby the action of an air stripper 64, which blows air through a series ofaligned nozzles against'the underside of the film at about thedesignated line 60. In practice, the conveyor is of aluminum and has a14x16 mesh (224 holes to the square inch). It is wider than the width ofthe film and moves at about twice the lineal speed of the surface of thewheel or about'three feet per minute. As it moves, it slips beneath thefilm as it is being stripped from off the wheel. The film is thoroughlydriedby air which is heated within an oven housing 66, the air beingdrawn in through the two open ends of the oven by a motor driven pump 68and discharged at a suitable'location. The oven has within it finnedelectric resistance rods 69, like those within the box 50. The conveyoris made of the mesh material so as a, be sureto obtain an undersurfaceon the film which 'is free of-bumps and unevennesses. Also the meshstructure. of the conveyor permits free access of the heated air to bothsurfaces of the film as it is being transported by the" conveyor.

The dried film is wound up on a spool 70 in any conventional fashion,care being taken that there always is sufiicient slack between theconveyor 62 and the spool 70 to avoid rupture of the film. i r

The mounting of the hopper with relationship to the casting wheel andits adjustment relative thereto is of extreme importance in attaining aproper consistent thinness of film cast on the wheel.

In the form of invention adopted to secure the best results, the hopper10, see Fig. 3, is constructed of a vertical rear end wall 81 fastened,as by bolts 81, to the substantially triangular side walls 82, 84extending laterally from an inclined front wall 86. The wall 86 inclinesdownwardly and toward the rear end wall 80 to form a metered orifice orslot at the bottom of the hopper. The hopper is closed at the top bymeans of a.

cover plate 83, removably held to the hopper by a pair of wing nuts 90threaded onto bolts 91 passing through slotted cars 92 on the cover andheld in blocks 94 fastened to the triangular side walls. Additionallythe cover is provided with threaded inlet 96 for pipe 14 and with valve12 to release air pressure, when desired, from within the hopper.

The bottom of the inclined wall 8-6 is rounded to rest in a groove 100of a metallic shoe 102 provided with side runners 104 shod with hardhighly polished shoes 105 which ride on the periphery of the wheel nearthe lateral edges thereof. The shoe is, in general, a casting comprisedof a thick cross piece 106 whose forward end is of less thickness, asshown at 108 and provided with the previously referred to arcuate groove100 to provide the seat for the rounded lower end of the front wall 86.The shoe also comprises the side runners 104 to straddle the formed filmand arcuate on their lower facesto conform with the curvature of theperipheral polished surface of the wheel. The rear end of the shoeconsists of a round bar 116) joining the runners to provide space,actually much more than needed, for the swing of wall 80 as the hopperis pivoted about the groove 100. The lower edge of wall 80 has a lip 112formed thereon to assist in placing an even film on the wheel and tocooperate with the lower thin portion 108 of the shoe to form a castingmouth 113. At the ends of the mouth, the Wall 80 is slightly recessed,as indicated at 114 to enable a Wide film to be cast.

The shoe is restrained against movement around with the circumference ofthe wheel by a pair of reach bars 115 pivoted on a shaft 116 fixed incars 118 on a bracket 120 fixed to a fixed part 121 of the machine, thebars having hooked ends 122 engaging pins 124 extending laterally fromthe side runners.

To micrometrically tilt the hopper about the groove 100 in. order tobring the lower edge 112 of wall 80 at a desired elevation, thefollowing instrumentalities are employed: Above the surface of the wheel22, the front wall 86 of the hopper has screwed thereto a bracket 130within which is fastened a cross pin 132. Pivotally mounted on the pinand straddling the bracket is a forked nut 134 interiorly threaded asindicated at 136. Extending upwardly and in a forwardly inclineddirection from the bracket is an arm 138 forked at its upper end andsupporting a pair of trunnions 1490f a second nut 142 within slots 144formed in the upper forked ends of the arm 138. The threads in the nuts134 and 142 are pitched slightly differently in the same direction andengage a complementarily threaded screw 146 having a knurled knob 148 onits end. Thus normal rotation of the knob 148 results in micrometrictilting of the hopper about the groove 106 as a center. For some casesit is essential to maintain a distance of .001 inch between the lip 112and the circumference of the wheel and it has been found that thearrangement just described can make the fine adjustment necessary. Sincethe shoe rides the wheel directly under lip 112 and the hopper rests onthe shoe, the distance between lip and wheel periphery is maintainedconstant even were the wheel to vary in diameter and not be a perfectcylinder.

The subject matter relating to the stripping of the film from the wheeland subsequent drying thereof is not the invention of the applicantsherein and is claimed in an application filed of even date herewith inthe names of Robert L. Lambert and William R. McKeirnan, assignors tothe assignees of the instant application and bearing Serial Number783,787.

What is claimed as new is:

l. Mechanism for casting a film onto a continuously moving supportcomprising a shoe resting on said support, mechanism restrainingmovement of the shoe along with the support, a hopper having downwardlyconverging side walls to form a mouth at the lower end of the hopper forfeeding material therewithin onto the moving support, means pivotallysupporting the lower edge of one of the said walls on said shoe, andmeans for tilting the hopper about said lower edge to adjust thethickness of material fed from the mouth of the hopper onto the movablesupport.

2. Mechanism for casting a film onto a continuously moving supportcomprising a shoe resting on Said support, mechanism restrainingmovement of the shoe along with the support, a hopper having downwardlyconverging side walls to form a mouth at the lower end of the hopper forfeeding material therewithin onto the support, means pivotallysupporting the lower edge of one of the said Walls on said shoe, an caron one of inclined walls of the hopper, a nut pivotally mounted in saidcar, a base for the mechanism, a second nut pivotally mounted on thebase, said nuts being provided with differential threads and acomplementary differentially threaded screw traversing the nuts formicrometrically tilting the hopper about said lower edge.

3. Mechanism for casting a film onto a continuously moving supportcomprising a shoe resting on said support, a base mounting the support,a link pivotally connected to said base and also pivotally connected tosaid shoe to allow movements thereof in a direction perpendicular to thesupport but to restrain movements of the shoe along with the continuousmovement of the support, a hopper having downwardly converging sidewalls to form a mouth at the lower end of the hopper for feedingmaterial therewithin onto the moving support, means pivotally supportingthe lower edge of one of the side walls on said shoe,

and means for tilting the hopper about said lower edge to adjust thethickness of material fed from the mouth of the hopper onto themovablesupport.

4. Mechanism for casting a film onto a continuously moving supportcomprising a shoe resting on said support, mechanism restrainingmovement of the shoe along with the support, a hopper having downwardlyconverging side walls to form a mouth at the lower end of the hopper forfeeding material therewithin onto the moving support, said shoe having athinned portion near the mouth, the upper surface of which has anarcuate groove, the lower edge of one of the said side walls beingrounded and pivoted in said groove, and means for tilting the hopperabout said lower edge to adjust the thickness of material fed from themouth of the hopper onto the movable support.

5. Mechanism for casting a film onto the cylindrical periphery of awheel comprising a shoe provided with arcuate runners riding on thearcuate surface near the edge of the wheel, said shoe having a memberwith a thin portion extending transverse to the arcuate runners, anarcuate groove in the upper surface of the thin portion along the lengththereof, a hopper having downwardly converging side walls to form amouth at the lower end of the hopper for feeding material in the hopperonto the periphery of the wheel between the runners, one of the sidewalls having a rounded lower edge resting in said groove, and means fortilting the hopper about said lower edge to adjust the thickness ofmaterial fed from the mouth of the hopper onto the wheel.

References Cited in the file of this patent UNITED STATES PATENTS2,842,797 Scherer July 15, 1958 FOREIGN PATENTS 368,886 Great BritainMar. 17, 1932

